1. Field of the Invention
This invention relates to the field of automatic signal switching for audio systems and in particular to a switching system responsive to a performer's vocal or instrument microphone, including a dead air timer arrangement automatically inserting a secondary program in the event of inactivity on the primary audio circuit.
2. Prior Art
Voice operated switched are known for controlling tape recorders and the like. In typical voice operated switching systems, the initiation of a signal on a voice line is detected and causes immediate commencement of recording. Upon cessation of activity on the line, the voice operated switch allows the recorder or the like to record for a further timed period selected to be longer than a delay typical of ongoing speech. If speech resumes during the delay, recording continues. Accordingly, the recorded information is automatically edited to reduce the length of gaps. An example of a voice operated switch can be found in U.S. Pat. No. 4,625,083--Poikela. While voice operated switch devices are useful for recording, they do not address the problem of audio switching in connection with live performance situations, where gaps in a program cannot be edited away.
A typical live performer such as a piano player in a lounge or the like, will play for a given length of time, for example an hour, and take a short break, for example fifteen minutes. During the break, it is useful for the benefit of patrons to provide a back-up audio program, which may or may not be of a similar type to the live program of the performer. Typically, the performer or a technician is expected to switch on a secondary signal source at the beginning of a break and switch off the secondary source when the program resumes. In many situations such as professionally-operated audio systems operated by audio technicians, the performer must strictly adhere to a regular schedule. According to plan, the audio technician punctually arrives to initiate the background program, and returns later to turn off the background program as the performer returns. Should the performer fail to adhere to a regular schedule or be required for whatever reason to take an unscheduled or irregular break, the background music may be unavailable or the audio technician's time may be wasted.
The present invention relates to a switch device included a dead air timer retriggerable at each instance of detected signal activity on the primary audio line. The primary audio line in this context may be a life performer's vocal microphone, an instrument microphone signal, or may be some other form of primary audio signal to be employed whenever available, and superceding other signal sources. For this purpose, an automatic switch is used not merely to start or stop tape recorders or players and the like, but to gate the respective signals through to a mixer and to determine based upon activity in the primary signal which of the signals is to be mixed and played. Preferably, the invention is used together with a mixer having a plurality of input channels, with the switched secondary source being routed to a different channel than the primary source and the connection between the secondary source and its channel being made through a controlled connection.
In connection with video switching devices, it is known to provide a storage means for storing the last scan line or last entire frame, and to re-insert the last line or last frame in the event a malfunction is detected in the transmission of a current line or frame. While it may also be possible to automatically switch among various video sources in the event of a malfunction in one, such a switching system is not responsive to activity on a primary line, such activity being present in any event.
In connection with audio switching systems generally, it is known to employ various switching techniques and various sensors and amplifiers in order to develop switching criteria for enabling certain systems. For example, U.S. Pat. Nos. 4,596,033--Swinbanks and 4,589,137--Miller involve switched enabling of audio signals responsive to detection of noise activity on a channel, the switched-in signal being an out-of-phase version of the background noise intended to be summed together with the basic signal to cancel or reduce noise levels. U.S. Pat. No. 4,596,021--Carter, et al, also involves a switching system allowing a telephone modem to switch back and forth between voice and data communications. Disclosures such as these, and voice operated switches such as Poikela lack means for automatic switching in both directions between alternative sources as needed to automatically produce a background music program or the like during gaps in live performances.
Instrumental performers frequently dispose a bank of switchable effects modules in series between their instruments and their amplifiers. These are adapted for manual control and switchably alter the primary signal or simply pass the primary signal. Such modules do not typically interact between channels and do not time dead air on one line for switching another line onto the output.
According to the invention, a switching system for detecting gaps in live performances and for switching in a secondary signal source upon detection of a long gap, is provided as a switching device to be inserted in series with both the primary and secondary input lines, leading to a multi-channel mixer. The switching system passes the primary to one mixer channel and upon dead air time-out, connects the secondary signal to another channel. In order to allow power to pass backwards, from the mixer to the audio signal source, for powering condenser microphones and the like (i.e. phantom power), the device is AC coupled to one or both signal lines through a high pass filter. An amplifier having a preferably adjustable gain in order to set the minimum level to be interpreted as "activity" is operated together with a second amplifier. The second amplifier preferably operates in saturation, providing a digital pulse train during periods of activity and either a high or low level during inactivity. A phase selection switch allows the user to invert the digital pulse train from the second amplifier if necessary, to produce low-going pulses on the output, indicating activity. A retriggerable timer having a preferably-adjustable time period determined by charging of a capacitor through a resistor is connected to a transistor conducting during the negative-going pulses, the transistor being thereby operable repeatedly to discharge the timing capacitor and thereby retrigger the timer during periods of activity. Upon time-out, the timer output drives a relay which connects the secondary or "controlled" signal to a second input channel of the mixer or the like.